Acids and Alkalis
Let us see about Acids and Alkalis. Lemon juice and vinegar taste sour because they contain weak acids. An ACID is a substance that dissolves in water to form positively charged particles called hydrogen ions (H+). The opposite of acid is an ALKALI which dissolves in water to form negatively charged ions of hydrogen and oxygen called hydroxide ions (OH-). Alkalis are ANTI ACIDS because they cancel out acidity. Toothpaste, for example, contains an alkali to cancel out acidity in the mouth that would otherwise damage teeth.
The concentration of hydrogen ions in a solution is known as its pH. Scientists use the pH scale to measure acidity and alkalinity. On the pH scale, a solution with a pH lower than 7 is acidic and a solution with a pH greater than 7 is alkaline. Water is neutral with a pH of 7. A solution’s pH can be tested with universal indicator solution or paper which changes color in acids and alkalis.
The more hydrogen ions an acid forms in water, the stronger it is, and the lower its pH. Strong acids, such as sulphuric acid and nitric acid, are very dangerous and must be handled carefully.
Concentrated sulphuric acid will dehydrate (remove water from) any substance with which it comes into contact. For example the acid dehydrates sugar, a carbohydrate, to leave a mass of smoldering black carbon.
Organic matter, such as paper, cork rubber, fabric and skin, is rapidly decomposed by nitric acid. The acid is so corrosive because it oxidizes (supplies oxygen to) any material with which it comes into contact.
Swedish scientist Svante Arrhenius (1859 – 1927) won acclaim for his research into how compounds form ions in solution. This work led him to realize that it is hydrogen ions that give acids their special properties.
Acids and Metals:
Even the weakest acids cannot be stored in metal containers because acids are corrosive to most meals. When an acid reacts with a metal, hydrogen gas is given off and the metal dissolves in the acid to form a compound called a salt. The reaction is very violent with metals such as potassium and sodium, and quite vigorous with metals such as magnesium and zinc.
When the hydrogen in an acid is replaced by a metal during a chemical reaction, a neutral compound called a salt is formed. For example, when copper reacts with nitric acid, the copper takes the place of the hydrogen to make the salt copper nitrate. Like other metals, copper forms a variety of salts when mixed with different acids. Most salts are crystals and many are colored. Some salts, such as sodium chloride (Common salt), occur naturally.
Acids are widely used in industry because they react so readily with other materials. For example, Sulphuric acid is used in the production of dyes and pigments, artificial fibers, plastics, soaps and explosives. The acid is made by sulphur and oxygen reacting together.
Burning fossil fuels to produce energy for use at home and in industry releases polluting gases into the air. The gasses dissolved in water in the clouds to form nitric acid and sulphuric acid. This water falls as acid rain, which erodes stone building and statues, kills trees and aquatic life and reduces the soil’s fertility.
Bases and Alkalis:
The acidity of vinegar (ethnic acid) can be neutralized or canceled out, by adding chalk (Calcium carbonate). Any substance that neutralizes acidity, such at chalk, is called a BASE. An alkali is a base that dissolves in water. An alkali’s strength is measured by the number of hydroxide ions it forms in water. Strong Alkalis, such as sodium hydroxide, are just are corrosive as strong acid.
Soaps and detergents:
Alkalis are good at dissolving oil and grease, so they are widely used in the manufacture of soaps and detergents. Most dirt is bound to skin, clothes or eating utensils by grease. The grease makes it difficult to remove the dirt with water alone, because water and grease do not mix. A soap or detergent, such as washing up liquid, breaks the grasses up into tiny drops and allows the water to wash away the dirt.
Acids, alkalis, and salts are electrolytes, meaning that they conduct electricity when in solution. Batteries consist of an electrolyte – usually in the form of a moist paste or liquid between two rods or plates called electrodes. The most common battery is the dry cell, which uses the salt ammonium chloride as an electrolyte. Long – life batteries contain alkaline electrolytes, such as potassium hydroxide. Car batteries have electrolytes of sulphuric acid.
The main raw material in the alkali industry is BRINE (Salt water). Sodium hydroxide, which is used to make soaps and paper, is produced from brine by electrolysis (passing electricity through it). Brine will also absorb carbon dioxide to make sodium carbonate which is used in textile treatment, photography and glass making.
Accidents with oil tankers at sea can create huge oil slicks (spillages) on the water’s surface. Detergents called dispersants are used to break up the oil and reduce environmental damage. Wildlife experts also use detergents, such as washing up liquid, to clean the feather of oil – coated seabirds. If the birds’ feathers – which usually keep them warm and dry – become clogged with oil, the birds may lose their buoyancy and drown, or die of exposure to the cold.
The main raw material in the alkali industry is brine (Salt water). Sodium hydroxide, which is used to make soaps and paper, is produced from brine he electrolysis (passing electricity through it). Brine will also absorb carbon dioxide to make sodium carbonate, which is used in textile treatment, photography, and glass making.
An alkali and an acid react together to give a neutral salt. In addition, hydroxide ions (OH-) in the alkali combine with the acid’s hydrogen ions (H+) to produce water (H2O). In daily life, problems of unwanted acidity are solved by adding an alkali of the appropriate strength.
The PH of soil varies from area to area. Few crops grow well in highly acidic soil, because the acid dissolves vital minerals that the plants need for healthy growth and allows them to be washed away. Farmers treat acidic soil by spreading lime (Calcium oxide) over their fields. This is a cheaply produced alkali made from limestone. It neutralizes the acid in the soil, making it more fertile.
The human stomach uses hydrochloric acid to break down food. Some foods cause your stomach to produce so much acid that it gives you discomfort. Stomach powders or indigestion tablets can cure this. They contain weak alkalis that neutralize the acidity, but do not harm your stomach or react too vigorously with the acid.
Bee and Wash Sting:
A bee sting is painful because it is acidic. Treating the sting with a weak alkali, such as soap or bicarbonate of soda, relieves the pain by neutralizing the acid. In contrast, a wasp sting is alkaline, so it can be neutralized by a weak acid such as vinegar or lemon juice.
In 1908, the German Chemist Fritz Haber (1868 – 1934) developed a process for making the alkali ammonia which is used to make fertilizers and explosives. The Haber process involves reacting nitrogen from the air with hydrogen at high pressure and temperature. Haber later devised a way of making nitric acid by heating ammonia in air.
c 600 BC: The Phoenicians use alkaline wood ash to make soap.
11th century AD: Arab chemists make sulphuric, nitric and hydrochloric acids.
1780s: World’s first sulphuric acid factory opens in France.
1865s: Ernest Solvay, a Belgian chemist, develops the first commercially successful process for making the alkali, sodium carbonate, on a large scale
1887: Svante Arrhenius proposes that it is hydrogen ions that give acids their special properties.
1980: Fritz Haber invents a process for making ammonia.
1909: The Danish chemist Soren Sorensen (1868 – 1939) devises the pH scale.
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